1. Technical Field
The present invention relates to an optical device, an analyzing apparatus and a spectroscopic method.
2. Related Art
In recent years, the demand for a sensor used for medical diagnosis, food inspection or the like has increased, and the development of a highly sensitive small sensor has been requested. In order to meet such a request, various types of sensors including one using an electrochemical method have been studied. Among these, interest in a sensor using surface plasmon resonance has increased because the sensor can be integrated, manufactured at low cost, and used in any measurement environment.
For example, JP-A-2000-356587 discloses a method in which sensor sensitivity is improved by using localized surface plasmon resonance caused by a substrate having fine metal particles fixed on the surface thereof.
JP-A-2007-10648 and JP-A-2009-250951 are other examples of the related art.
When the intensity of Raman scattering is enhanced by using an electric field that is enhanced by surface plasmon resonance, and the target sensing sensitivity is improved, the degree of electric field enhancement is determined by the product of the degree of electric field enhancement at an excitation wavelength and the degree of electric field enhancement at a Raman scattering wavelength. Thus, in order to improve the sensing sensitivity, it is necessary to increase both the degree of electric field enhancement at the excitation wavelength and the degree of electric field enhancement at the Raman scattering wavelength.
For example, in the method of JP-A-2000-356587, since it is difficult to equalize the sizes of the fine metal particles and their arrangements, variations occur in the resonant wavelength, and the width of an absorbance spectrum becomes broad. Further, only one resonant peak occurs. Thus, for example, when sensing a rare target, it is difficult to obtain a sufficient degree of electric field enhancement in both the excitation wavelength and the Raman scattering wavelength.
Incidentally, JP-A-2007-10648 discloses a localized plasmon resonance sensor having a resonant peak shifted to a longer wavelength side and a resonant peak shifted to a shorter wavelength side. JP-A-2009-250951 discloses an electric field enhancement device in which a micro resonator is constructed of plural resonant areas in order to enable resonance to occur at plural wavelengths.